Fallen stock indexes are expected weigh on the third-quarter earnings of big asset managers, showing how market turmoil can affect a broad swath of financial companies.

The Standard & Poor's 500 index fell 14 percent during the quarter, finishing at 1,131.42, on growing concerns about Europe's debt crisis and the U.S. economic and political outlook.

The index has come back a bit since then, but the drop cut into asset managers' share prices and led some analysts to reduce their earnings estimates for big managers like BlackRock Inc and Legg Mason, knowing that lower markets will leave them with fewer assets under management against which to charge fees.

These businesses can't drop their expenses fast enough to offset the sharp declines in revenue, said KBW analyst Robert Lee. He said he was not predicting the companies would turn to layoffs soon, even though personnel are usually a company's highest expense.

In a research note last week Lee lowered his estimates for how much the group would earn by 6 percent on average from estimates he issued in early September.

Another analyst, Craig Siegenthaler of Credit Suisse, said in a recent note to investors that market uncertainties have had another effect, de-risking, such as driving money away from the equity funds that traditionally were among the companies' most profitable products.

Data from Chicago research company Morningstar bears out that idea. Investors withdrew a net of $45.7 billion from long-term mutual funds in the quarter, with U.S. stock funds accounting for nearly all the outflow. On the other hand, low-cost exchange traded funds took in an estimated $19.7 billion in the quarter, Morningstar said.

SEASON STARTS OCT. 19

An earnings report from the largest asset manager, BlackRock Inc, will start the season on October 19, followed by T. Rowe Price Group on October 25 and Franklin Resources Inc on October 27.

A hint of what is to come came October 13 when JPMorgan Chase & Co issued third-quarter earnings that included its own asset-management unit. There, net income of $385 million was down 8 percent from the same period a year ago and down 12 percent from the second quarter of 2011.

This is a business that was clearly ... affected by volatile markets this quarter, said Doug Braunstein, JPMorgan's chief financial officer, on a conference call with analysts. Though revenue of $2.3 billion was up 7 percent from a year ago, it fell 9 percent from the second quarter.

The asset-management business, Braunstein continued, is one in which we would expect to see continued pressure on revenue in the fourth quarter if the current market conditions persist.